Tim Hunt

Looks like you have tried a lot of good debugging arleady, and not yet found any useful clues.

In the Browser developer tools, can you switch to the 'Network' tab, and try it again. Can you see the request to Moodle that leads to the 'Undefined' message? Does looking at the information about that request show anything useful?

In your head? In your institution?

You can use it for whatever you like, and people use it for all sorts of different things.

That seems very odd.

I am wondering if this is some strange visual glitch, for example, doe the choices contain bulleted list items, and are those then getting laid out badly, with the bullet overlapping the radio button?

Can you edit the question, and the look at the HTML source for the choices in the editor, to try to see what is going on?

Agreed, but still might be a good idea to developer the code, and get it to a good place, in plugin land, and then land it in core.

That is a standard part of Moodle, I think. In the quiz, Results -> Statistics.